It has long been established that the continuous monitoring of various bodily ionic characteristics over extended periods of time provides data useful in the evaluation of disease. For example, diagnosis of gastroesophageal disorders, such as inflammatory disease or lower esophageal sphincter incompetence, may be made by the monitoring of esophageal pH over time. The earlier devices developed to perform such monitoring employed an electrode inserted through the nasal passage into the esophagus, a reference electrode in contact with the patient's skin, an electrical shock isolation module through which the signal from the electrodes and the patient were electrically isolated from monitoring instruments, and a pH meter and recording apparatus receiving, displaying and recording the isolated signal.
These devices effectively tether the patient to the pH meter and recorder because the electrodes and pH meter must be wired together by electrical conductors. With such a restricted range of movement, the patient's activities must be similarly circumscribed, resulting in data, generally known as a reflux pattern, that is not usually a true reflection of what generally occurs during the patient's ordinary activities.
More recently developed devices employed in the monitoring of pH in the distal esophagus have attempted to overcome this significant deficiency by radiotelemetering pH data from portable transmitting equipment carried by the patient to stationary radio receiving and recording instruments. One such device converts the esophageal pH signal to one that can be transmitted using a commercially available electrocardiogram (ECG) signal radiotelemetry system. Although this approach does permit the patient a much greater zone of freedom of movement than afforded by earlier devices (in the range of several hundred feet), and consequently does result in somewhat more accurate reflux patterns, the patient's mobility is still restricted.
Several additional drawbacks exist in known systems for monitoring esophageal pH over extended periods of time. The output signals from certain pH electrode types, as the renowned two millimeter diameter glass electrode, have a tendency to drift over extended periods of operation, introducing varying errors in the resulting reflux patterns. Inasmuch as different pH electrode types possess differing electrical output characteristics, heretofore monitoring systems were limited to operation with one type of pH electrode with which they were designed to operate. Also significant is that existing esophageal pH monitoring systems universally provide a reflux pattern in the form of a waveform output from a strip-chart recorder which require "reading" and interpreting by persons possessing a specialized and high level of skill. The scarcity of such trained medical personnel makes this task an additional burden and often results in undesirable delays in reaching a diagnosis.